1. Field of the Invention
The present invention relates to an optical storage medium such as an optical disk or optical card, a data recording and reproducing apparatus for recording, reproducing, and deleting data on the optical storage medium, and a tilt detection apparatus for detecting the angle between the optical storage medium and a light beam converged by a convergent system in the data recording and reproducing apparatus.
2. Description of Related Art
Optical storage technologies using optical disks having a pattern of pits for recording data as a high density, high capacity storage medium have found applications ranging from recording digital audio and video to document filing systems and computer data file storage. Digital Versatile Disks (DVD) read with a 650 nm visible wavelength semiconductor laser as the light source have in particular recently become popular because of their high density storage capacity, and standards for read-only DVD-ROM media, write-once DVD-R media, and multiply rewritable DVD-RAM media have been established.
FIG. 15 shows the configuration of the optical system of a prior art optical pickup head system for reading DVD-ROM media as exemplary of an optical storage medium. The light source, a semiconductor laser 1, emits a divergent beam 70 of linear polarized light with a wavelength xcex=0.65 xcexcm. The divergent beam 70 is reflected by half mirror 7, bending the light path so that the beam 70 passes a collimator 8 with a 20 mm focal length and is converted to parallel light. The parallel beam 70 is then converted to a convergent beam by a 3 mm focal length objective lens 9, passes the transparent layer 40a and converges on the data recording surface 40b of the storage medium 40. The aperture of objective lens 9 is restricted by aperture 12 to a numerical aperture NA of 0.6. The thickness of the transparent layer 40a is 0.6 mm.
The beam 70 reflected from the data recording surface 40b passes the objective lens 9 and collimator 8, then passes the half mirror 7 and astigmatism is introduced. The beam 70 then passes a concave lens 11 with a tilted optical axis, thereby correcting the astigmatism and coma introduced when the beam 70 passed the half mirror 7, and is received by a photodetector 31. Axis 31e is parallel to the image of the recording track on data recording surface 40b in the beam received by the photodetector 31.
The photodetector 31 has four receiving parts 31a to 31d, each outputting a current signal 131a to 131d according to the amount of light detected. Each of the receiving parts 31a to 31d is 50 xcexcmxc3x9750 xcexcm. The current signals 131a to 131d output from the receiving parts 31a to 31d are respectively input to circuit part 51a to 51d of current-voltage conversion circuit 51, converted thereby to a voltage signal V51a to V51d, and output from the optical pickup head system.
A focusing error signal is calculated from the signals V51a to V51d output from the optical pickup head system using an astigmatism method, that is, as (V51a+V51c)xe2x88x92(V51b+V51d). When the medium is a DVD-ROM as in this example, a tracking error signal is obtained using a differential phase detection (DPD) method comparing the phase of V51axcx9cV51d; if the medium is a DVD-RAM, the tracking error signal is calculated using a push-pull method, that is, by calculating (V51a+V51d)xe2x88x92(V51b+V51c). The focusing error signal and tracking error signal are amplified to a desired level and phase-compensated, then supplied to actuators 91 and 92 for focus and tracking control.
If the numerical aperture NA of the objective lens 9 is increased to 0.6, it will not be possible to faithfully read data recorded to the storage medium 40 if warping of the storage medium 40 is great. The angle between the storage medium 40 and converged beam 70 is therefore detected using a reflection photocoupler.
This reflection photocoupler consists of light source 97 and photodetector 98. The light source 97 is a light-emitting diode. The receiving part of the photodetector 98 is divided into two parts. The signal strength of the output from the two receiving parts of the photodetector 98 varies according to the tilt of the storage medium 40. It is therefore possible to obtain a signal corresponding to the tilt of the storage medium 40 by differentially amplifying the signals output from the photodetector 98. Though not shown in the figure, the beam 70 is constantly controlled to a desired angle relative to the storage medium 40 regardless of how the storage medium 40 is warped by inclining the entire optical system, including the photocoupler and optical pickup head system, using this signal corresponding to the tilt.
However, when the warp of storage medium 40 is detected using a reflection photocoupler, the cost of the optical system is necessarily increased as a result of the additional parts and the additional steps needed for assembly.
Furthermore, because the track to which the beam used for tilt detection is emitted and the track to which the beam is emitted for reading data are different, it is not possible to sufficiently correct tilt of the optical storage medium if the tilt differs according to the position in the radial direction, and faithful signal reproduction may not be possible.
To resolve the problems associated with using a photocoupler for tilt detection, Japanese Patent Laid-Open Publication (kokai) H10-97753 (U.S. patent application Ser. No. 08/877363), Kokai 2000-57606, Kokai 2000-90948, Kokai 2000-123390, Kokai 2000-137923, Kokai 2000-149296 (U.S. patent application Ser. No. 09/386458), Kokai 2000-149298, and Kokai 2000-123390 (U.S. patent application Ser. No. 09/386458) teach a tilt detection apparatus using the DVD-RAM guide groove and the CAPA address area. This tilt detection apparatus does not require a photocoupler, and simplifies the optical design.
When a photocoupler is used for tilt detection, closed loop control is not possible without driving the entire optical system, including the photocoupler, and adjusting for tilt to the optical storage medium. The problem is that because the entire optical system is driven, adaptation to a thin data recording and reproducing apparatus is difficult.
Furthermore, because tilt detection using the guide groove and CAPA is effective when the pitch Gp of the guide groove formed on the optical storage medium is greater than xcex/NA, more data can be recorded and good tilt detection can be achieved when tracks are formed on both lands and grooves as in DVD-RAM media. However, if a data track is provided in only the land or the groove, data recording capacity drops if Gp greater than xcex/NA so that good tilt detection can be achieved, and if Gp less than xcex/NA so that data recording capacity is increased, good tilt detection cannot be achieved.
Considering the problems of a prior art apparatus as described above, an object of the present invention is to provide an optical storage medium, a tilt detection apparatus using the optical storage medium, and a data recording and reproducing apparatus using the tilt detection apparatus such that when a tilt detection apparatus is used to detect optical storage medium tilt, stable detection of optical storage medium tilt is possible by means of a simple configuration when the guide channel pitch is decreased in order to increase data storage capacity.
To achieve the above object, an optical storage medium according to the present invention having guide grooves with a pitch of Gp1 between adjacent grooves has intermittent grooves Gnxe2x88x921 and Gn+1 adjacent to opposite sides of an n-th groove Gn with non-groove spaces formed in grooves Gnxe2x88x921 and Gn+1, creating an area where pitch Gp2 of groove Gn is equivalent to twice pitch Gp1 so that xcex/NAxe2x89xa7Gp1xe2x89xa7xcex/(2xc2x7NA) where xcex is the wavelength of a beam emitted for recording or reproducing data, and NA is the numerical aperture of the convergent system for converging the beam on the optical storage medium.
A further optical storage medium having guide grooves with a pitch of Gp1 between adjacent grooves according to the present invention has an intermittent groove formed with non-groove spaces therein, forming an area where groove pitch Gp2 is equivalent to twice pitch Gp1 so that xcex/NAxe2x89xa7Gp1xe2x89xa7xcex/(2xc2x7NA) where xcex is the wavelength of the beam emitted for recording or reproducing data, and NA is the numerical aperture of the convergent system for converging the beam on the optical storage medium.
A yet further optical storage medium having guide grooves with a pitch of Gp1 according to the present invention has an intermittent groove Gnxe2x88x921 or groove Gn+1 adjacent to opposite sides of an n-th groove Gn formed with non-groove spaces in groove Gnxe2x88x921 or Gn+1, creating an area where groove pitch Gp2 is equivalent to greater than twice pitch Gp1 so that xcex/NAxe2x89xa7Gp1xe2x89xa7xcex/(2xc2x7NA) where xcex is the wavelength of the beam emitted for recording or reproducing data, and NA is the numerical aperture of the convergent system for converging the beam on the optical storage medium.
A tilt detection apparatus according to this invention has a laser light source for emitting a beam; a convergent system for converging the beam emitted from the light source to a small spot on a data recording medium, i.e., an optical storage medium; a photodetector for detecting the beam diffracted and reflected by the optical storage medium and outputting a signal according to the light quantity of the detected beam; and a signal processor for receiving a first signal and a second signal output from the photodetector and processing the received signal to output a signal related to the angle formed between the optical storage medium and optical axis of the convergent system. The optical storage medium has a guide groove with a pitch of Gp1 between adjacent grooves, groove Gnxe2x88x921 and groove Gn+1 adjacent to opposite sides of an n-th groove Gn both being intermittent grooves with nongroove spaces formed therein, providing an area where pitch Gp2 of groove Gn is equivalent to twice pitch Gp1 so that xcex/NAxe2x89xa7Gp1xe2x89xa7xcex/(2xc2x7NA) where xcex is the wavelength of the beam emitted for recording or reproducing data, and NA is the numerical aperture of the convergent system for converging the beam on the optical storage medium. The pitch of the groove on the optical storage medium when the first signal is obtained is Gp1, and the pitch of the groove on the optical storage medium when the second signal is obtained is Gp2.
A similarly configured tilt detection apparatus according to a further aspect of this invention detects tilt between the emitted light beam and an optical storage medium having guide grooves with a pitch of Gp1 between adjacent grooves, an intermittent groove being formed with non-groove spaces therein, providing an area where groove pitch Gp2 is equivalent to twice pitch Gp1 so that xcex/NAxe2x89xa7Gp1xe2x89xa7xcex/(2xc2x7NA) where xcex is the wavelength of the beam emitted for recording or reproducing data, and NA is the numerical aperture of the convergent system for converging the beam on the optical storage medium. The pitch of the groove on the optical storage medium when the first signal is obtained is Gp1, and the pitch of the groove on the optical storage medium when the second signal is obtained is Gp2.
A tilt detection apparatus according to a yet further aspect of this invention and also configured as described above detects tilt between the emitted light beam and an optical storage medium having guide grooves with a pitch of Gp1 between adjacent grooves, groove Gnxe2x88x921 or groove Gn+1 adjacent to opposite sides of an n-th groove Gn being an intermittent groove with non-groove spaces formed therein, providing an area where groove pitch Gp2 is equivalent to greater than twice pitch Gp1 so that xcex/NAxe2x89xa7Gp1xe2x89xa7xcex/(2xc2x7NA) where xcex is the wavelength of a beam emitted for recording or reproducing data, and NA is the numerical aperture of the convergent system for converging the beam on the optical storage medium. The pitch of the groove on the optical storage medium when the first signal is obtained is Gp1, and the pitch of the groove on the optical storage medium when the second signal is obtained is Gp2.
A data recording and reproducing apparatus according to this invention has a tilt detection apparatus as described; a drive unit for changing a relative position between the optical storage medium and tilt detection apparatus; and an electric signal processor for receiving and processing a signal output from the tilt detection apparatus to obtain desired information stored on the optical storage medium.
It is therefore possible to detect relative tilt between an emitted light beam and an optical storage medium using an operation on two signals obtained from guide grooves with different groove pitchs even when the guide groove pitch is reduced and recording capacity increased. It is therefore possible to provide a highly reliable data recording and reproducing apparatus.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.